Freiraum und Mikroklima

The aim of this project was to develop planning foundations and design guidelines for climate-sensitive and energy-efficient urban planning, with a focus on the interface between buildings and adjacent open spaces. The interactions concerning (micro-)climate were investigated.

The starting point was the determination of macroclimatic conditions. Small-scale model simulations were conducted by the project partner AIT – Department Foresight & Policy Development using two regional climate models. The goal was to provide data for an average year and a hot year. For building physics calculations, hourly data for relevant parameters for two years of current climate and two years of future climate (2041-2050) were extracted: temperature, precipitation, global radiation, cloud cover, relative humidity, wind direction, and speed. Additional indicators on a daily or monthly basis were derived, such as climate comfort indices.

To develop models for subsequent simulations and their plausibility checks, knowledge of microclimatic open space effects was essential. The fundamental mechanisms between open space and microclimate were determined on the two scales of the entire settlement and individual open spaces. Existing studies and research projects were analyzed based on a literature review to provide criteria for selecting reference spaces in AP3 and for simulations in AP5. Furthermore, materials characteristic of urban open space were categorized based on their specific microclimatic properties. The results were compiled into a data catalog to support the development of transformation functions and simulations.

In order to find an effective and scalable way to derive microclimatic conditions in the immediate vicinity of buildings from weather station data (preferably unaffected by building details), transfer functions were developed and tested. These transfer functions allowed the derivation of structurally relevant microclimatic variables (radiation intensity, temperature, humidity, wind speed) from standardized weather station data.

Reference spaces were defined considering suitable combinations of building geometry, surface characteristics, open space design, and construction execution (e.g., insulation type). This was followed by the modeling of buildings and open spaces using simulation tools for (i) building energy demand (for heating and cooling: active building operation scenarios), (ii) thermal comfort conditions within buildings (passive summer building operation scenarios), and (iii) outdoor conditions (immediate surroundings of the buildings).

The identified relationships between overall surface design (open space and building surfaces), energy efficiency of buildings, and quality of stay were summarized in a catalog of measures. The respective results were compiled in a timely manner for developer competitions and open space design and communicated to the planning teams.

Conclusions on Project Results:

1. The results indicate that, in the case of heavily insulated building envelopes, the external surface design has a minimal impact on building heating and cooling loads. The most significant differences were observed with the use of shading-effective rows of trees along the facade, leading to up to 20% lower cooling loads for the simulated buildings. Similar results were achieved with effectively applied external shading.

2. Simulation results for the years 2040-2050 (with projected climate change) suggest that future heating loads are expected to decrease (by about 15%), while cooling loads are likely to increase significantly (by about 23%). These findings imply that cooling energy consumption could dominate in the future. Currently, active cooling is not required in Austrian residential buildings. If this changes due to warming, energy consumption could increase substantially. This highlights the importance of appropriate measures to reduce this trend and incorporate it into current urban planning.

3. Simulation scenarios with different resolutions of weather data show that cooling and heating load results can differ by up to 10%. This emphasizes the importance of considering building microclimate for accurate and reliable simulation results.

4. Heating load results for different orientations show that a south-facing window orientation performs slightly better. However, for the same building, the lowest cooling loads were achieved with a north-facing orientation. As primary orientation in a cardinal direction is often not practical, combined orientations (i.e., north and south or east and west, as well as intermediate cardinal directions) were evaluated. The results show slightly better performance for buildings with a north/south orientation compared to east/west orientation.

5. Results for different street widths imply that buildings with wider streets result in lower heating loads, while narrower streets lead to lower cooling loads. Cooling loads of buildings adjacent to wider streets can be reduced by rows of trees (or other shading measures).

6. For thermal comfort in open spaces, a high proportion of greening measures, particularly through deciduous tree plantings, is desirable for shading and thus dampening temperature increases during heatwaves, as well as for wind protection. In general, maximizing vegetation and water surfaces should be pursued, and surface sealing should be avoided.

Final report

• Freiraum und Mikroklima